A wheel bearing apparatus is generally known that can support a wheel of vehicle with respect to a suspension apparatus and incorporating a rotational speed detecting apparatus to detect a rotation speed of a wheel of a vehicle to control the anti-lock braking system (ABS). In such a bearing apparatus, a sealing apparatus is arranged between inner and outer members that rotate relatively to each other, via rolling elements contained between them. The sealing apparatus is integrally formed with a magnetic encoder with magnetic poles alternately arranged along its circumference. The rotational speed detecting apparatus includes the magnetic encoder and a rotational speed sensor to detect the change of the magnetic poles of the magnetic encoder caused by the rotation of the wheel of the vehicle.
A rotational speed sensor is generally known that is adapted to be mounted on a knuckle that forms part of a suspension apparatus, after the wheel bearing apparatus has been mounted on the knuckle. A wheel bearing apparatus incorporating a rotational speed detecting apparatus has been proposed that can avoid the troublesome air gap adjustment between the rotational speed sensor and the magnetic encoder. Also, it contains the rotational speed sensor in the wheel bearing to reduce the size of the wheel bearing apparatus.
A known structure of a wheel bearing apparatus incorporating a rotational speed detecting apparatus is shown in FIG. 10. This wheel bearing apparatus includes an outer member 51, forming a stator member and adapted to be secured to a knuckle (not shown), and an inner member 52. The inner member 52 is arranged in the outer member 51 via double row balls 53, 53. The inner member 52 includes a wheel hub 55 and an inner ring 56 fit onto the wheel hub 55.
The outer member 51 has an integrally formed body mounting flange 51b on its outer circumference. The outer member inner circumference includes double row outer raceway surfaces 51a, 51a. The inner member 52 is formed with double row inner raceway surfaces 55a, 56a. The inner raceway surfaces 55a, 56a oppose the double row outer raceway surfaces 51a, 51a of the outer member 51. One inner raceway surface 55a of the double row inner raceway surfaces 55a, 56a is formed on the outer circumference of the wheel hub 55. The other inner raceway surface 56a is formed on the outer circumference of the inner ring 56. The inner ring 56 is press-fit onto the cylindrical portion 55b that axially extends from the inner raceway surface 55a of the wheel hub 55. The double row balls 53, 53 are contained between the outer and inner raceway surfaces and are rollably held herein by cages 57, 57.
The wheel hub 55 is integrally formed with a wheel mounting flange 54, for mounting a wheel (not shown), on one end. The inner ring 56 is axially immovably secured by a caulked portion 58. The caulked portion 58 is formed by plastically deforming the end of the cylindrical portion 55b. A seal 59 and a sensor cap 63 are mounted on the ends of the outer member 51. The seal 59 and sensor cap 63 prevent leakage of lubricating grease sealed within the bearing and entry of rain water or dust from the outside of the bearing.
A magnetic encoder 60 is press-fit onto the outer circumference of the inner ring 56. The magnetic encoder 60 includes an annular supporting member 61. The supporting member 61 has a substantially L-shaped cross-section. An encoder body 62 is adhered to the side of the annular supporting member 61. The encoder body 62 has N and S poles alternately arranged along its circumference.
The sensor cap 63 is fit into the inner circumference of the inner-side end of the outer member 51 to close the opening of the outer member 51. The sensor cap 63 includes a bottomed cylindrical cap body 64, formed by injection molding synthetic resin, and an annular metallic member 65. The annular metallic member 65 is press-formed from a steel sheet to have an annular configuration with a substantially L-shaped cross-section. The metallic member 65 is integrated with the cap body 64 during injection molding of the cap body 64.
An axially projected portion 66 is formed on the cap body 64 at a radially outer portion. A sensor receiving bore 67 is formed in the projected portion 66 at a position corresponding to the magnetic encoder 60. As shown in FIG. 11, a sleeve 68 is fit into the sensor receiving bore 67. A sensor 69 is further inserted into the sleeve 68, via an O-ring 70. The sensor 69 includes an IC circuit incorporated with a magnetic detecting element 71. It senses changing characteristics in accordance with the direction of flux such as a Hall element, a magnetic resistance element (MR element) etc. A waveform shaping circuit, for shaping the output waveform of the magnetic detecting element 71, is included. It forms the ABS of an automobile to detect the rotational speed of a wheel and to control it.
A mounting portion 72 projects from the sensor 69. The mounting portion 72 has a bolt inserting aperture 73. A sleeve 74 is fit in the aperture 73. The sensor 69 can be mounted on the cap body 64 by screwing a sensor securing bolt 75, inserted into the sleeve 74, into an inserted nut 76.
The cap body 64 and the sensor 69 are formed of low water absorption plastic materials such as PA (polyamide) 612, PPS (polyphenylene sulfide) etc. Thus, dimension variations and the generation of cracks, that would be otherwise caused by absorption of the sensor mounting member, can be prevented. The sealability can also be maintained (see Japanese Laid-open Patent Publication No. 2007-120560).
A prior art wheel bearing apparatus incorporating a rotational speed detecting apparatus has the sensor 69 inserted into the sensor receiving bore 67 formed in the projected portion 66 of the cap body 64, via the O-ring 70. The O-ring 70 would be bit between the sensor receiving bore 67 and the sensor 69. Thus, it would be damaged during insertion of the sensor 69. In addition, it is believed that the sensor 69 would be urged to its eccentric position in the sensor receiving bore 67 when the sensor securing bolt 75 is screwed into the inserted nut 76. Thus, the interference of the O-ring 70 would be uneven and the sealability would be extremely detracted. Accordingly, muddy water would enter into the wheel bearing through the sensor receiving bore 67.
Furthermore, the sensor receiving bore 67 of the cap body 64 is kept exposed until the sensor 69 is inserted into the sensor receiving bore 67 during assembly by an automobile manufacturer. Thus, some foreign matter would be led into the wheel bearing through the sensor receiving bore 67. Accordingly, it is necessary to close the sensor receiving bore 67 by using any type of sealing member, such as a plug, before assembling the sensor 69 into the wheel bearing apparatus.